hey guys, alittle background.

car is fully built 10.5.1, 2.0 6266bb turbo. acording to a tuner, he says my fuel pressure is unstable. now i did find a problem with my FRP which is a fuelab. the diaphram was torn. i have a double pumper, 400 and 255 intank. after going from a ams1000hp kit, which includes a 255 inline and a 255 intank. i swapped the 255 intank for a 400 and the 255 inline i left it. but i made more logs and pressure acording to a tuner was still crazy. so i then decided to do a intank setup, after a week i finally went intanks, and i jus logged again and it seems to be the same.

now i dont know how "unstable" unstable is according to him. but i seems to have my setup going well. -6an from pumps to a -8, and for return i have the factory feed with siphon drilled out... base pressure was set to 50 psi, witht eh other pump kicking in at 50 percent gas

can someone look at this or maybe post up a similar log so i can compare. im only running at WG pressure which is i think 25psi

LOG: <<<<<<<<<<<<<<AFTER FPR WAS FIXED >>>>>>>>>>> Green is Fuel Pressure, Orange is AFR






<<<<<< THIS WAS BEFORE FPR DIAPHRAM WAS FIXED>>>>>>>>>
green is fuel pressure, orange is afr's

 

wow no one? some info? im sure if i put buschur or something someone would be all over it lol...

 

fuel pressure at the rail should always be the sum of intake manifold and base fuel pressure (determined by measuring fuel rail pressure at idle with the vacuum line disconnected from the fpr). for example, if boost is holding steady at 30 psi, and base pressure is 43 psi, then rail pressure should be 73 psi.

this means that an easy way to determine if rail pressure is acceptable is to tell your aem to log rail pressure minus boost. that value ought to be equal base pressure at all times. if it jitters by more than 3 psi peak-to-peak, then there's a problem.

 

bro im lost on whats next, i have swapped pumps, new fpr rebuilt, better lines, and im done... the sensor before had said my pressure was up to 150 psi before. so i swapped the location, i moved it from the rail to the regulator.... so now it reads better. but after that i have no idea

 

logging at the rail is fine. if rail minus boost is not steady, then assuming that your sensor is not broken and is wired correctly, there is a fuel supply issue. i guess that's self-evident.

fprs are usually pretty reliable, so i'd focus first on the pump setup. since you have a double pumper, the first thing to check would be the hobbs switch. it might be working intermittently. operation of the hobbs switch can be verified by piercing the pump power wires at the tank with needles and then have someone observe voltage with a dvm while you drive. do it for both pumps.

 

pm sent bro

 

well the pumps are set my aem ems to come on at 50 percent throwttle. i can hear it kick on and off.... before i had them run all the time, but rail pressure would not go lower than 63. so i staged it..... so once you say to probe the pumps, what voltage is a no go if i have someone look at it? what am i looking for?

 

good move to trigger it with the aem. if those pressure variations are more than 5 psi at steady boost, i could imagine that you'd see pretty big voltage swings, like more than a few volts.

 

thanks man... but now, so do a pull lets in 3rd and see how the voltage looks like? or just normally driving? seems from the logs it looks like only once im at high rpm and going into boost... any ideas or tips are welcomed!

 

During boost when fuel pressure becomes erratic.

 

so what would cause voltage drop like that ? anything to check while im logging, other than volts at the pump

 

Well, it may not just be a voltage drop or a lack of voltage at the pump/connections. That is a good place to start. However, if it is custom wired, check all connections and splices. You can send 100,000 volts through 1 strand of wire but it may only be able to produce .5 amp. Since fuel pumps draw higher amperage, you should check all the connections. This would be why you rewire fuel pumps with larger gauge wire to flow higher amperage to the pump for the additional demand in power/amperage.

 

so from batt to relay lets say 10 gauge, than from relay to pump 14?